Contaminated, degraded or incorrect transmission fluid restricting solenoid movement; Pressure control solenoid B sticking mechanically or failed internally; Blocked or clogged transmission filter or valve body passages with debris; Wiring or connector fault between the solenoid and the transmission control module, such as chafing, corrosion or a short to power; Worn valve body or sticking spool valve causing uncontrolled pressure; Faulty transmission control module driver circuit; Low or high fluid level causing pressure irregularities.

P0777

Pressure Control Solenoid B Stuck On.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
7: AreaTransmission
77: FaultThe specific fault in that area

What it means

P0777 means the transmission control module has detected that Pressure Control Solenoid B is stuck on, so it is delivering hydraulic pressure when it should not or cannot be reduced. The module saw a mismatch between the commanded line or clutch pressure and the actual result, such as unexpected gear ratio, slip or flare. Which clutch circuit solenoid B controls depends on the make, model and gearbox.

Symptoms

Harsh or abrupt gear changes
Gearbox stuck in one gear or default limp mode
Flare or slip between gear changes
Transmission warning light or engine warning light on
Poor acceleration or reduced shift quality
Delayed or no engagement in some gears

Possible causes

Contaminated, degraded or incorrect transmission fluid restricting solenoid movementlikely
Pressure control solenoid B sticking mechanically or failed internallylikely
Blocked or clogged transmission filter or valve body passages with debrispossible
Wiring or connector fault between the solenoid and the transmission control module, such as chafing, corrosion or a short to powerpossible
Worn valve body or sticking spool valve causing uncontrolled pressurepossible
Faulty transmission control module driver circuitrare
Low or high fluid level causing pressure irregularitiespossible

How to diagnose

Read all stored and pending codes and note the freeze frame data, including gear, temperature and vehicle speed at the time of setting
Check the transmission fluid level, condition and smell, following the manufacturer's procedure for the specific gearbox, as some are sealed or need a set temperature
Inspect the transmission wiring harness and connectors for damage, fluid ingress, corrosion and chafing
Check for related codes and any technical service bulletins for the model and gearbox
Use live data to compare commanded and actual solenoid current or pressure and watch gear ratio during shifts
Measure the solenoid resistance and check the supply and control circuits against the manufacturer's specification
Inspect the fluid and pan for metal or clutch material, and check the filter
Remove and inspect the valve body and solenoid for sticking or wear if the electrical checks pass

How to fix

Replace the transmission fluid and filter with the correct specification if it is contaminated or degraded
Repair or replace damaged wiring and connectors in the solenoid circuit
Replace the faulty pressure control solenoid B or the solenoid pack, as the design requires
Clean or overhaul the valve body, or replace it if the bores are worn
Correct the fluid level to the specified amount
Repair or replace the transmission control module only after the wiring and solenoid have been proven good

Can I keep driving?

High severity

Avoid driving beyond what is needed, as a solenoid stuck on can cause harsh engagement, slipping and clutch damage, and the gearbox may drop into limp mode. Have it checked promptly and avoid towing or heavy loads.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.